Catalysts for olefin polymerization or copolymerization are well known in the literatures. These catalysts typically comprise a transition metal-containing active component, generally comprising magnesium, titanium and halogen as main ingredients; a cocatalyst component, typically organo-aluminium compound; and external electron donor component, typically organo-silicon compound. For stereoelective polymerization of olefin, especially stereoelective polymerization of propylene, if no external electron donor component is used, most of these catalysts give a polymer having lower isotacticity, typically lower than 90%, so that they are not applicable to industrial scale production. Therefore, the addition of external electron donor component is often necessary.
At preset, the types of external electron donor compounds have developed from initial benzoates to current organosiloxane. For instance, WO 00/63261 discloses external electron donor compounds useful in olefin polymerization, i.e. silicon compounds having a general formula R11aR12bSi(OR13)c, wherein a and b are integer from 0 to 2, c is integer from 1 to 3, and the sum of a+b+c is 4, R11, R12 and R13 are independently C1-C18 hydrocarbyl which optionally contains heteroatom. The preferred are those silicon compounds in which a is 1, b is 1, c is 2, at least one of R11 and R12 are selected from the group consisting of branched alkyl, alkenyl, alkylene, cycloalkyl and aryl, having from 3 to 10 carbon atoms and containing optionally heteroatom, and R13 is C1-C10 alkyl, especially methyl, for example, cyclohexylmethyldimethoxysilane. The also preferred are those silicon compounds in which a is 0, b is 1, c is 3, R12 is branched alkyl or cycloalkyl, containing optionally heteroatom, and R13 is methyl, for example, cyclohexyltrimethoxysilane and the like.
It is noted that, among the silicon compounds having the general formula R11aR12bSi(OR13)c, those silicon compounds wherein c is 1 are generally not deemed as good external electron donor compound. In the prior art, γ-trihydrocarbylsilyloxy ether compounds have never been used as external electron donor compounds in olefin polymerization. However, the inventors have surprisingly found that, when used as external electron donor compounds in olefin polymerization, especially in propylene polymerization, γ-trihydrocarbylsilyloxy-ether or -silicon ether compounds exhibit good properties, for instance, the catalyst system exhibits good hydrogen responsibility, and can be used to prepare polymer having high isotacticity at high yield.